In a UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, Long Term Evolution (LTE) has been under study.
In the third-generation mobile communication system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable bandwidth from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems to LTE have been under study (for example, LTE Advanced (LTE-A)). For example, in LTE-A, there is a plan to expand the maximum system band of the LTE specifications, which is 20 MHz, to approximately 100 MHz. Also, the maximum number of transmitting antennas according to the LTE specifications is planned to be expanded from four antennas to eight antennas.
Also, in a system of the LTE scheme, a MIMO (Multi Input Multi Output) system is proposed (see, for example, non-patent literature 1), as a radio communication technique to transmit and receive data by a plurality of antennas and improve the data rate (spectral efficiency). In the MIMO system, a plurality of transmitting/receiving antennas are provided in the transmitter/receiver, so that different transmission information sequences are transmitted at the same time from different transmitting antennas. On the other hand, on the receiver side, taking advantage of the fact that fading variation is produced between the transmitting/receiving antennas, by separating and detecting the information sequences that have been transmitted at the same time, it is possible to increase the data rate (spectral efficiency).
In a system of the LTE scheme, single-user MIMO (SU-MIMO), in which all the transmission information sequences that are transmitted from different transmitting antennas are directed to the same user, and multiple-user MIMO (MU-MIMO), in which transmission information sequences that are transmitted from different transmitting antennas are directed to different users, are defined. In these SU-MIMO transmission and MU-MIMO transmission, on the receiver side, an optimal PMI is selected from a codebook, in which a plurality of sets of an amount of phase/amplitude control to be set in the antennas of the transmitter (precoding matrix (precoding weight)) and a PMI (Precoding Matrix Indicator) to be associated with the precoding matrix, are defined, per rank, and fed back to the transmitter, and, furthermore, an RI (Rank Indicator) to indicate an optimal rank are selected fed back to the transmitter. On the transmitter side, based on the PMI and RI fed back from the receiver, the precoding weight for each transmitting antenna is specified, precoding is performed, and transmission information sequence is transmitted.